As a technique to improve an output of an engine, a method (supercharging) of compressing intake air with a supercharger and supplying an engine with the compressed intake air is known, and widely used in an engine for an automobile and the like. A supercharger may be transitionally in an abnormal operational state with surging, over-speed, or the like, depending on the operational state of the supercharger. Such abnormal operation may lead to breakage of various devices, and should be prevented as much as possible.
Patent Document 1 discloses an invention, which is a control device for a turbocharger, for suppressing surging by predicting occurrence of surging from an operational state of a turbocharger and opening a waste-gate valve immediately before occurrence of surging to reduce a flow rate of exhaust gas flowing to a turbine.
Patent Document 2 discloses an invention, which is a supercharging control device, for suppressing surging by providing a compressor-bypass valve for returning intake air from a downstream side toward an upstream side of a compressor and closing the bypass valve to return intake air if occurrence of surging is predicted.
Patent Document 3 discloses an invention, as a control device for a variable geometry turbocharger, for suppressing over-speed of a turbocharger by changing a vane angle of nozzle vanes to achieve the maximum nozzle area in case of over-speed.